Conventionally, in order to reduce burden on drivers driving vehicles, steering assist devices have been developed, each of which gives, to a steering, an auxiliary torque for assisting a steering force of a driver in accordance with a traveling state of a vehicle. As a type of such steering assist devices, a steering assist device has been developed, which gives, to a steering, an auxiliary torque so as to keep the position of a vehicle in a lane in which the vehicle travels. This steering assist device is known as a so-called LKA System (Lane Keeping Assist System).
An example of the above-described steering assist devices is disclosed in Patent Literature 1. A steering control device disclosed in Patent Literature 1 calculates a lateral target acceleration of a vehicle, which is required for the vehicle to travel in the center of a lane in which the vehicle travels. Then, the steering control device gives, to a steering, an auxiliary torque which is required for the lateral acceleration of the vehicle to reach the target acceleration. When the steering control device calculates the target acceleration, the steering control device controls the target acceleration by performing feed-forward control based on the curvature of the lane in which the vehicle travels. Further, the steering control device controls the target acceleration by performing feed-back control based on, for example, a distance from the center line of the lane in which the vehicle travels to the vehicle. According to the feed-forward control and the feed-back control, the torque of the steering is controlled so that the vehicle travels in the center of the lane, along the lane.
According to the control by the above-described steering assist device, even when the vehicle is performing lane change, that is, even when the vehicle intentionally leaves the lane in which the vehicle currently travels, an auxiliary torque that brings the vehicle back to the center of the lane might be generated. So, generally, the above-described steering assist device halts generation of an auxiliary torque while a direction indicator mounted on the vehicle is being operated.